grep sed and a loop Post: 302521630

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Top Forums UNIX for Dummies Questions & Answers grep sed and a loop Post 302521630 by agama on Thursday 12th of May 2011 12:21:22 AM

05-12-2011

Registered User

Here is a simple example of how to process a log file and save the last line for reference on the next run. It uses the entire last line from the log as the reference point, rather than a date/time stamp. Less efficient, but more accurate. I'm sure there are other ways to make this more efficient, but this might help get you started.

It does run in Kshell. Should run in bash, but for several reasons I prefer Kshell and didn't test it under bash, so beware if you want to use this as a bash script.

Code:

#!/usr/bin/env ksh


logf=$1                 # log file to suss; supplied as parameter on cmd line
pat=$2                  # pattern to search log for
this=${0##*/}           # base name of script
lastf=/tmp/$this.data   # file where we tuck our last found line away for next time

if [[ -z $logf || -z $pat ]]        # error if logfile name or pattern isn't supplied
then
    echo "usage: $0 log-file-name pattern"
    exit 1
fi

if [[ ! -s $lastf ]]    # no last run data; must check all lines from log
then
    need_all=1          # this will cause us to check for pattern straight away
fi

# parse the log file writing, to stdout, any matches that haven't been seen yet
# The last line seen is written to the last data file for next time.
#
awk  -v snarf=$need_all -v lastf=$lastf -v pat=$pat '
    BEGIN {
        if( !snarf )                # not in check all mode, must find last data
        {
            getline < lastf;
            last_data = $0;
            close( lastf );
        }
    }

    snarf {                         # need all, or found the last line from prev run
        if( match( $0, pat ) )      # if it contains the pattern, print it to stdout
            print;
        new_last = $0;              # save the last line we saw
        next;                       # go to next input line (skip remaining awk code)
    }

    {       # not snarfing yet, check to see if this is the last line we saw before
        snarf = $0 == last_data;    # start snarfing if it matches
        # tricky way of saying:
        # if( $0 == last_data)
        #     snarf = 1;
    }

    END {
        if( new_last )
            printf( "%s\n", new_last) >lastf;   # save our last observed line in the data file.
    }
' <$logf

exit $?           # return the exit code that awk returned with

The one thing this script doesn't do is to deal with the case where the log file has been rolled off. In this case the data file would be non-empty, but we'd need to start checking for the pattern at the start of the log rather than after the previous marker is encountered.

The easy solution to this is to remove the last data file when the log is rolled. If that's not possible, then additional code will be needed to detect this condition; beyond my few minutes to spend answering questions tonight -- sorry.

If you need some info about awk, this is a decent set of doc:
Awk - A Tutorial and Introduction - by Bruce Barnett
and there are other posts on this forum that link other sites.

Hope this helps.

agama

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LEARN ABOUT DEBIAN

snarf

snarf(1)						      General Commands Manual							  snarf(1)

NAME

       snarf - Simple Non-interactive All-purpose Resource Fetcher

SYNOPSIS

       snarf [-avqprzm] URL [outfile] ...

DESCRIPTION

       Retrieves data from a variety of protocols, namely http, ftp, and gopher.

USAGE

       snarf is invoked with any number of URLs and outfiles. If an outfile is not specified, snarf preserves the remote file name when saving.

       For  example, snarf http://foo.bar.com/images/face.gif will retrieve the file ``face.gif'' to the local system.	In the event that there is
       no filename (the url ends in a slash), the data is retrieved and stored in the file index.html for http URLs, ftpindex.txt for ftp URLs, or
       gopherindex.txt for gopher URLs.

       Using a dash, "-", as the outfile causes snarf to send its output to stdout rather than a file.

       To log in to an ftp server or website that requires a username and password, use the syntax http://username:password@site.com/. If you omit
       the password, you will be prompted for it.

       Snarf has a built-in option to download the latest version of itself; simply run snarf LATEST.

   OPTIONS
       -a     Causes snarf to use "active" ftp. By default, snarf uses passive ftp, and, if the server does not support it, falls back	to  active
	      ftp. Using the -a option will avoid the initial passive attempt.

       -r     Resumes an interrupted ftp or http transfer by checking if there is a local file with the same name as the remote file, and starting
	      the transfer at the end of the local file and continuing until finished. This option only works with HTTP  servers  that	understand
	      HTTP/1.1 and ftp servers that support the REST command. snarf uses this option automatically if the outfile already exists.

       -n     Don't resume; ignore the outfile if it exists and re-transfer it in its entirety.

       -q     Don't print progress bars.

       -p     Forces  printing	of progress bars. Snarf has a compile-time option for whether progress bars print by default or not. The -p option
	      overrides the -q option. In addition, if progress bars are enabled by default, snarf suppresses them when standard output is  not  a
	      terminal. Using -p will override this behavior.

       -v     Prints all messages that come from the server to stderr.

       -z     Send a user-agent string similar to what Netscape Navigator 4.0 uses.

       -m     Send a user-agent string similar to what Microsoft Internet Explorer uses.

       Each option only affects the URL that immediately follows it. To have an option affect all URLs that follow it, use an uppercase letter for
       the option, e.g. -Q instead of -q.

ENVIRONMENT

       Snarf checks several environment variables when deciding what to use for a  proxy.  It  checks  a  service-specific  variable  first,  then
       SNARF_PROXY, then PROXY.

       The service-specific variables are HTTP_PROXY, FTP_PROXY, and GOPHER_PROXY.

       Snarf also checks the SNARF_HTTP_USER_AGENT environment variable and will use it when reporting its user-agent string to an HTTP server. In
       the same spirit, it also uses the SNARF_HTTP_REFERER environment variable to spoof a Referer to the web server.

BUGS

       Bugs? What bugs? If you find 'em, report 'em.

AUTHOR

       Copyright (C) 2000 Zachary Beane (xach@xach.com)

								    17 Jun 2000 							  snarf(1)

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